Xylene separation with liquid hf and tif4



July 13, 1954 D. A. MCCAULAY ET AL XYLENE SEPARATION WITH LIQUID HF AND TIFq.

Filed Feb. 20, 1952 mm\% m @t d assoc/W005i@ INVENTORSI David A. McCall/ay Arf/wr R Lie/7 U LJ nlllL ATTORNEY Patented July 13, 1954 XYLENE SEPARATION WITH LIQUID HF AND TiF4 David A. McCaulay, Chicago, Ill., and Arthur P. Lien, Highland, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application February 20, 1952, Serial No. 272,654

12 Claims. 'i

This invention relates to a process for the selective separation or concentration and recovery of certain lower dialkylbenzenes from their mixtures with other lower dialkylbenzenes, which mixtures may also contain monoalkyl benzenes, benzene and saturated hydrocarbons. In one specific form, this invention relates to a process for the selective separation or concentration and recovery of individual xylene isomers from narrow boiling range aromatic hydrocarbon fractions containing the same. This invention relates more particularly to a process for the selective separation or concentration of metaxylene from narrow boiling range aromatic hydrocarbon fractions containing meta-xylene, para-xylene, ethylbenzene and saturated hydrocarbons boiling in the boiling range of the xylene fraction and normally associated with said xylenes as produced by hydrocarbon conversion processes; the aromatic hydrocarbon fractions may also contain ortho-xylene.

The boiling points and freezing points of the xylenes, and of ethylbenzene which boils within the same range, are

B. P., F.1 F. P., "172l Ortho-xylene 291A 95 13. 32 Meta-xylene 282. 38 54. 17 Para-xylene. 281. 03 +55. 87 Ethylbenzene 277. 14 138. 96

tain an ortho-xylene concentrate containing A more than about 70% ortho-xylene by superfractionation from xylene fractions containing saturated hydrocarbons boiling in the same range, due to overlapping boiling ranges of azeotropes of the various xylenes with the saturated hydrocarbons. Para-xylene has been separated from mixtures thereof with meta-xylene by fractional freezing, which is an expensive and laborious procedure compared with the process of the present invention. Fractional freezing or melting is severely handicapped, even disregarding economic considerations, by the fact that paraand meta-xylenes form a eutectic mixture containing about 88 weight percent metaand 12 weight percent para-xylene (M. P, 73 F.) and n paraxylene cannot be selectively frozen from mixtures containing less than about 16% paraxylene (U. S. Patents, 1,940,065 and 2,398,526 and British Patent 585,076).

One object of our invention is to provide processes for the selective separation or concentration of individual xylene isomers from mixtures of xylene isomers. An additional object of our invention is to provide processes for the selective separation or concentration and recovery of meta-xylene from mixtures thereof with paraxylene or ortho-xylene or from mixtures containing all three isomeric xylenes. Yet another object of our invention is to provide a process for the separation of a mixture of xylenes or concentrates of individual xylene isomers from ethylbenzene.

A further object of our invention is to provide a process for the separation of xylenes from mixtures thereof with benzene and monoalkylbenzenes, particularly toluene and ethylbenzene. Still another object of our invention is to provide a process for the separation of a mixture of isomeric xylenes from associated, close boiling saturated hydrocarbons, following which individual xylene concentrates are produced by the process of this invention.

Another important object of our invention is to provide a practical process for the concentration of individual xylene isomers from xylene fractions such as are normally produced by hydrocarbon conversion operations or by the extraction of petroleum fractions. The above and other objects of our invention are achieved by the process whose details are set forth below.

We have discovered that by the joint employment of liquid HF and TiF4 as a selective reaction solvent under appropriately selected operating conditions, it is possible to achieve the selective extraction of certain meta-dialkylbenzenes from other dialkylbenzenes and less-alkylated benzene hydrocarbons.

We have also discovered that ethylbenzene, which is usually associated with xylenes as produced in hydrocarbon conversion processes, undergoes disproportionation with surprising ease in the presence of liquid HF and TiF4 to produce chiefly benzene and diethylbenzenes and, in the presence of xylenes, ethylxylenes. The disp-roportionation of ethylbenzene is of immense value in simplifying its separation from xylenes and makes it possible thereafter to separate selectively or to concentrate individual xylene isomers from each other by means of liquid HF and TiF4, without interference by ethylbenzene.

We have also found that isomeric xylenes may be substantially completely extracted from a mixture of xylenes and saturated hydrocarbons of the same boiling range by contacting said mixture with a molar excess of liquid hydrogen fluoride and with 'IiF4 in at least a bi-molar ratio of TiF4 to xylenes. Benzene and toluene are not particularly soluble in the liquid HF-TiFr treating agent, with the result that xylenes may be extracted from mixtures thereof with benzene and toluene (as well as saturated hydrocarbons) by the employment of liquid HF and 'I'iF4 in an amount which is at least bi-molar with respect to the xylenes present in said mixture.

The mechanism by which the liquid HF-TiFi treating agent functions appears to be by the formation of a complex. The complex formed by a lower dialkylbenzene contains 2 mols of TiF4 and (at least) 1 mol of HF per mol of aromatic hydrocarbon. We believe the complex contains at least 1 mol or HF because no complex is formed by xylene or diethylbenzene when these are contacted with 'I'iF4 in the absence of liquid HF. Benzene, toluene and other monoalkylbenzenes do not form a complex with TiFi and HF at the temperatures of this process.

TiF4 is a crystalline solid having a boiling point or' 543 F. The solid is only slightly soluble in liquid HF. The solubility of TiF4 in liquid HF is enormously increased when a polyalkyl aromatic hydrocarbon is brought into Contact with the TiFi in the presence of liquid HF, e. g., a slurry of I'iF4 and liquid HF is rapidly converted to a clear reddish liquid when the slurry is contacted with a sufficient amount of xylene.

When the feed stock to our process consists of a lower dialkylbenzene wherein the alkyl radical contains between 1 and 5 carbon atoms, such as xylene, in admixture with non-aromatic hydrocarbons and/or benzene or toluene, contacting of said feed stock with a sumcient amount of our liquid HF-TiFf.. treating agent results in a raffinate phase and an extract phase. The extract phase consists of liquid HF, complex and some physically dissolved hydrocarbons. The degree of removal of the xylene from the feed is dependent upon the amount of TiFfx present in the treating agent. Substantially complete removal of the xylene can be achieved by using at least about 2 mols of TiF4 per mol of xylene present in the feed. In some cases, particularly when the ratio of non-complexible hydrocarbon to xylene is quite high, more than 2 mols of TiF4 per mol of xylene will be necessary to achieve substantially complete removal of xylene. The amount of TiF4 should be limited to about that amount which will be completely complexed or brought into solution in the extract phase. We have found that solid 'IiF4 present in the extract phase has a marked catalytic effect on the aromatic hydrocarbons in the extract phase and undesirable side reactions, such as,y isomerization, disproportionation and even cracking may occur; this effect is especially apparent when operating at higher temperatures. In general, while we may use from as little as 0.1 mol of TiFi per mol of dialkylbenzene in the feed to as much as 4 mols, we prefer to use between about 0.5 and 2.5 mols of TiF4 per mol of dialkylbenzene in the feed.

When monoalkylbenzenes, such as, ethylben zene, propylbenzene, isopropylbenzene, butylbenzene, etc. are present in the feed stock, the liquid I-LF-TiFfx treating agent catalyzes the rapid disproportionation of these compounds to dialkylbenzenes. The dialkylbenzenes form complexes with TiFi and pass into the extract phase. Therefore, when these monoalkylbenzenes are present in the feed stock, it is necessary to use sufficient TiF4 to complex .with the corresponding dialkylbenzene as well as with the lower dialkylbenzenc present in the feed stock itself, When ethylbenzene and/ or propylbenzene are present in the feed stock, we prefer to use l mol of TiF4 per mol of said compound in addition to that used for the lower dialkylbenzenes present in the feed.

The stability of the HF-TiF4 complexes formed by the ortho, meta and para-xylenes is quite different; the order of stability, in decreasing order, is meta, ortho and para-xylene. We have found that the relative order of stability as indicated by the equilibrium dissociation constants is about 20:2:1 for the complex formed by meta-xylene, ortho-Xylene, para-xylene with respect to para-xylene, respectively. When a substantially pure mixture of at least two xylene isomers is contacted with liquid HF--TiF4 treating agent, the ratio of more stable complex isomer to the other isomer(s) present is much higher in the extract phase than in the feed, and much lower in the raiinate phase than in the feed. The maximum degree of separation of a mixture of two isomeric xylenes is attainable by using about 2 mois of 'IiF4 per mol of the more stable complex isomer present in the feed. While a high purity meta-xylene, e. g., about cannot be separated from a mixture of xylenes in a single contacting stage, it is possible to achieve this result by using a multi-stage or countercurrent tower operation.

Suicient liquid HF must be present to participate in the formation of the complex and to dissolve the complex. We prefer to use an excess over this amount in order to insure the formation of a separate extract phase. In general, when operating with mixed feeds containing xylene, the use of about 5 volume percent of liquid HF based on the total feed will be sufcient to form a separate extract phase. As much as 500 volume percent of liquid HF or more may be used. In general the use of larger amounts of liquid HF assists in phase separation and also, surprisingly enough, decreases the amount of non-aromatic hydrocarbons present in the extract phase. We prefer to use between about and 300 volume per cent of liquid HF, based on total mixed feed. The liquid HF used in our process should be substantially anhydrous, i. e., the liquid HF should contain less than about 1 or 2% of water. In order to maintain the low water content of the system it may be desirable to dehydrate the feed to the process.

Temperature is an important factor in our process. When the contacting is carried out at temperatures in excess of about F., side reactions take place, such as, isomerization of meta-xylene to the equilibrium mixture of the three isomers and disproportionation of the xylenes to higher alkylbenzenes. When operating at tempera-tures below about 30 F., longer contact times are necessary to achieve good separations and, at temperatures below about 0 F., the disproportionation of ethylbenzene, etc. is slowed `down markedly, 'which is disadvantageous when treating ethylbenzene-containing feeds. Although we can operate at higher temperatures by using very short contact times and by quenching the reaction mixture at the end of the contacting, we prefer to operate below about 100 F. Under some conditions of temperature, T1F4 usage and long contact time, ortho and/or paraxylene are isomerized to the meta-xylene isomer. When it is desired to minimize this isomerization, not only should temperature be held at less than about 90 F., but also contact times should be short and the amount of TiF4 used should be such that a minimum amount of ortho and/or para-xylene are present in the extract phase.

Contacting times are dependent upon the temperature at which the contacting is carried out and upon the degree of agitation in the contacting zone. When using normal methods of agitation, contacting time may vary from as little as l minute to as much as 3 or more hours. In general, when operating at between about 30 and 90 F. and with a feed from which it is desired to remove substantially all the xylene isomers contained therein, a suitable contacting time is between about l minute and 30 minutes.

The extract phase is readily decomposed by treatment with water, preferably cold water or ice. The upper layer of extract oil can be decanted from the lower aqueous layer. The lower aqueous layer consists of a mixture of hydroiluorie acid and 'Iii-*4. The extract oil can be freed or" traces of HF by treatment with dilute aqueous caustic. This method is particularly suitable for laboratory operations.

We prefer to decompose the extract phase by distilling off HF in a decomposer which iS provided with a few fractionation trays. Normally the top temperature in the decomposer is held at about the boiling point of HF, at the particular pressure in the vessel, in order to prevent the removal or" extract oil along With the HF. After the removal of HF the bottom of the decomposer contains a slurry of extract oil and solid finely divided TiFi precipitate. This slurry is then passed to a lter which retains the solid T1134. The lowest possible temperature is maintained in the decomposer in order to avoid side reactions during the decomposition step. We prefer to operate the decomposer under vacuum in order to remove the major portion of the HF at temperatures below about 100 and more preferably, below about 70 F. In order to facilitate the distillation of the HF at low temperature, a hydrocarbon stripping agent which is inert to the catalytic effect of liquid HF at the temperature in the decomposer may 'oe introduced into the decomposer. Such stripping agents may be propane, butane, pentane, petroleum ether, etc.v

We have found that the organic sulfur compounds normally present to some extent in virtually all hydrocarbon mixtures form complexes with Tim and HF. In general, these sulfur compound complexes are more stable than the dialkylbenzene complexes and are more difiicult to decompose. However, heating the complex to temperatures on the order of 400 to 500 F. Will drive off the HF and thus dissociate the complex. It is possible to dissociate the dialkylbenzene complex without dissociating the sulfur compound complex. When operating with feed stocks containing moderate amounts of sulfur, such as, 0.2 wt. per cent, we can decompose the extract phase and separate the extract oil from the TiF4 and organic sulfur compound complex; this is possible because the sulfur compound complexes appear to be solid materials only slightly soluble in hydrocarbon oil. The TF4 can be recovered completely for reuse in the process .by heating the TiF4 and organic sulfur compound complex The TiEi can be reused in the process.

to about 400 and 500 F. in a second operation and driving olf the HF and organic sulfur compounds.

The alkylphenols which are normally present in cracked stocks also complex with Tilri and HF. These complexes tend to interfere with phase separation and also introduce undesired impurities into the extract oil. In order to eliminate this interference, feed stocks containing such alkylpheno-ls should be dephenolized by a suitable treatment, e. g., washing with 25% aqueous caustic solution.

The liquid HF-TiFi treating agent is a very powerful alkylation catalyst. The aromatic hydrocarbon compounds present in a feed stock containing olens are very readily alkylated to form monoalkylbenzene and polyalkylbenzene. Usually these polyalkylbenzenes are of a character different from the dialkylbenzenes present in the feed, and being of a much higher boiling point can be readily separated therefrom by simple fractional distillation. However', some of the feed dialkylbenzenes are lost by this alkylation resulting in a decreased yield based on dialkylbenzene present in the feed stock. For this reason we prefer a feed stock that is low in olens.

Our process may be applied to a mixture of hydrocarbons comprising aromatics, parafns, naphthenes and olefins which boil in the approximate boiling range of the particular dialkylbenzenes that are to be recovered. For reasons expressed above, We prefer a low sulfur feed stock such as one containing on the order of about 0.02 Wt. per cent sulfur. Also, we prefer a feed stock substantially free of alkylphenols.

A particularly suitable feed for our process is the naphtha derived from the so-called hydroforming process, i. e., from the vapor phase treatment of a virgin naphtha at 850 to 1050 F. in the presence of hydrogen over a catalyst such as molybdena on an alumina support or a platinum-containing catalyst. The hydroformate from such a process is low enough in sulfur to permit operation without further desulfurization and is sufficiently low in olen that little degradation of the desired xylene content results during the separation step.

Any hydrocarbon oil which contains appreciable amounts of lower dialkylbenzenes can be charged to our process either directly or after suitable pretreatment to lower the sulfur and alkylphenol content. These feed stocks may be derived from the distillation of petroleum, from the thermal or catalytic cracking of naphthas from petroleum, from the hydroforming or hydrodesulfurization of virgin or cracked naphthas, or they may be derived from the coking of coal or from the drip oil produced in the production of carbureted water gas or producer gas. Other sources of feed to our process are the highly aromatic extracts obtained by treating petroleum oils with selective solvents, such as,

phenol, furfural, SO2, and the like; usually these extracts will have to be desulfurized prior to treatment by our process. It should be understood that our process is applicable to the extraction of dialkylbenzenes and particularly the extraction of meta-dialkylbenzenes from isomeric dialkylbenzenes, regardless of the method by which the feed was prepared.

The more common feed stocks for our process are a mixture of dialkylbenzenes, non-aromatic hydrocarbons, benzene, toluene and ethylbenzene.

The non-complexible materials, i, e., non-aromatic hydrocarbons, benzene and toluene usually form from 50 to 75 volume percent of the total feed. (Monoalkylbenzenes other than toluene are not considered non-complexible materials because their disproportionation results in the formation of a complexible material, for example, diethylbenzene.) Where xylene concentrates are available from superfractionation equipment, a feed stock containing 70 or 80% of xylene and ethylbenzene may be available. We have found that phase separation and selectivity are improved when the feed stock does not exceed about 50 volume percent of complexible hydrocarbons. When operating on a substantially pure xylene and ethylbenzene mixture we prefer to add from about 50 to 200 volume percent of an inert hydrocarbon dluent. rhe diluent should be a parafnic and/ or naphthenic hydrocarbon or a mixture of hydrocarbons that is low in materials that would interfere with phase separation and that will be readily separable by simple fractional distillation from the individual aromatic hydrocarbons. We prefer to use as diluents paramnic and naphthenic hydrocarbons of low boiling point since these materials are not isomerized or cracked by the liquid HF at the preferred operating temperatures. Suitable hydrocarbons are butane, pentane, hexane, heptane, petroleum ether, etc. When operating at low temperatures such as 30 F. the diluents might be higher boiling paraiflnic or naphthenic hydrocarbons containing or 11 carbon atoms. In general, when treating a feed stock to remove substantially all the dialkylbenzenes, sufcient non-ccmplexible hydrocarbons will be present in the feed so that no additional diluent is needed. We prefer to operate with a minimum amount of non-complexible hydrocarbons, i. e., about one volume per volume of dialkylbenzene plus monoalkylbenzenes, other than toluene.

Our process is applicable to the dearomatization of a mixture of saturated aliphatic and/or naphthenic hydrocarbons With benzene and/or toluene. The benzene and. toluene are converted to dialkylbenzenes by alkylation with an olen, such asy ethylene or propylene, in the presence of a suitable catalyst. Liquid HF and TiF4 may be used as the catalyst; When using HF-TiF4 catalyst suiiicient agent must be present to complex with the dialkylbenzene formed, if substantially complete conversion and removal of benzene and/or toluene is desired. The dialkylbenzene-containing hydrocarbon mixture is then contacted, if HF-TiRr is not the catalyst, with a sufficient amount of our liquid HF-TiFr treating agent to remove substantially all the dialkylbenzenes, leaving a substantially aromatic-free saturated hydrocarbon raffinate oil.

The non-aromatic hydrocarbons extracted from the feed by the treating agent boil in about the same range as the aromatic hydrocarbons. Their presence decreases the purity of the aromatic hydrocarbons and they must be removed in order to obtain substantially pure aromatics as the final product. We havefound that these non-aromatic hydrocarbons can be readily displaced from the extract phase by washing the extract phase with an inert diluent non-aromatic type hydrocarbon such as pentane, hexane or a l0 or 11 carbon atom paraffin, A single stage washing operation is usually suicient to reduce the non-aromatic content of the extract phase to a point Where substantially pure aromatics can be obtained by simple fractional distillation of the recovered aromatic hydrocarbons.

Several examples of the results obtainable by our process are set out below. In all cases the contacting was carried out in a carbon steel reactor equipped with a 1725 R. P. M. stirrer. The experimental procedure was to add a quantity of TiF4 to the reactor, followed by liquid HF and then by the aromatic hydrocarbon-containing feed stock. The contents of the reactor were stirred for a selected time at a selected temperature; at the end of the contacting time the contents of the reactor were allowed to settle before withdrawing the contents. The lower extract phase was withdrawn into a vessel containing crushed ice; the hydrocarbons from the decomposed extract phase were decanted away from the aqueous layer. The hydrocarbons were washed with caustic to eliminate traces of HF and then were distilled in a 30-plate laboratory column to recover the various fractions. The purity and the compositions of the fractions were determined by a combination of ultraviolet and infrared analysis, boiling point, specific gravity and refractive index.

The raffinate phase was washed with aqueous caustic to remove entrained HF and was then analyzed for aromatic hydrocarbon content.

Run 1 (S1-74) rl`he feed to this run consisted of ml. (.80 mol) of meta-xylene and para-xylene, respectively. The inert hydrocarbon diluent was n-heptane--BOO ml. The treating agent consisted of 500 ml. of liquid HF and 1.38 mols of TiFr. Thus the mol ratio of TiF4 to xylenes was 0.86 and to meta-xylene wasl 1.7. The contents of the reactor were stirred for 30 minutes at a temperature of 37 F. The contents were settled for l5 minutes and then the extract phase and rafnate phase withdrawn separately. The n-heptane was stripped from the aromatic hydrocarbons in the raffinate phase and from the hydrocarbons in the extract phase. The raffinate aromatic hydrocarbons and extract aromatic hydrocarbons were analyzed by ultraviolet light technique and were found to be:

Composition, Mol Percent Raflinate Extract iii-Xylene 26 83. 6 p-Xylenc 74 16. 4

Analysis indicated that no hydrocarbons other than meta and para-xylene were present in the extract aromatic hydrocarbons. The mol ratio of xylenes to Tilr in the extract phase was 0.45 which is in good agreement with the 0.5 ratio determined by tests on substantially pure xylene isomers.

Run 2 matic hydrocarbons recovered from the two phases were analyzed and found to consist of:

Composition, Mol Percent Ranate Extract o-Xyiene 37 2O m-Xylene 70 p-Xylene 43 10 Rim 3 (S1-138) Composition, Mol Percent Raiiinate Extract o-Xyiene 24 5. 6 m-Xylene. ll 51.0 pXyiene 33 7. 6 Ethylbenzene 22 7. 6 Benzene 10 Cm Aromatics 28. 1

When operating on a mixed Ca aromatic hydrocarbon feed, substantially complete conversion of ethylbenzene is attainable only when no second rainate phase is present, i. e., no diluent can be present. In the presence of a diluent, the ethylbenzene passes into the raiiinate phase. The rate of conversion under these conditions, even when contacting is very effective, is quite slow and considerable unconverted ethylbenzene will be present in the raffinate phase after several hours of contacting.

Analysis of the C10 aromatic hydrocarbons indicated them to be mainly ethylxylenes. The very unexpectedly high content of ethylbenzene in the extract is believed to be the result of a side reaction which took place in the extract phase during the settling period. We believe that a slow reaction takes place in the extract phase between the diethylbenzene, formed by the disproportionation of ethylbenzene, therein and the xylenes therein. This reaction proceeds to form ethylxylenes, principally 1,3-dimethyl- 5-ethylbenzene and ethylbenzene. Ethylberb zene is somewhat soluble in the complex-containing extract phase; the ethylbenzene byproduct of the ethylxylene formation remained in the extract phase because the absence of agitation prevented the inert hydrocarbons from washing the ethylbenzene out of the extract phase as fast as it was formed. rThis adverse effect of ethylxylene formation can be very readily overcome by using a minimum settling time or by reducing the temperature of the mixture to about 30 F. However, in order to avoid this very undesirable side reaction, the extract phase should be decomposed at low temperature and without delay after the contacting step has been completed.

The figure shows an illustrative embodiment of our process. This iigure demonstrates the treatment of a narrow boiling fraction in the Xylene boiling range, i. e., 270 to 300 F. which has been derived from the hydroforming of a virgin naphtha. The aromatic hydrocarbon content of this feed stock is ethylbenzene, l2 mol per cent; ortho-xylene, 21 meta-xylene, 48; and paraxylene, 19%. The non-aromatic hydrocarbons of this feed amount to volume percent of the total feed. The process described in this preferred embodiment of our process removes all the xylenes from the feed and converts much of the ethylbenzene into benzene and metadiethylbenzene in a rst step, and in a second step separates the xylenes into separate high purity isomeric fractions. In this example high purity means in excess of mol per cent of the particular isomer.

In the first step of this process we show a tower-type of continuous countercurrent operation for the removal of substantially all the xylenes from the mixed feed. This tower can be packed with PIF-resistant materials, such as, Raschig rings, Berl saddles, alumina balls, etc. Although we show a tower operation, we are not limited to the use of a tower and can use a series cf batch countercurrent extraction zones. The separation factor for the removal of xylenes from non-complexible hydrocarbons is so great that in many cases a satisfactory degree of extraction can be obtained by a single stage contacting, i. e., only a single contactor and a settler are needed in the extraction Zone. We prefer to use at least two stages when removing substantially all the xylenes from a feed stock of this type.

The mixed feed from source il is passed by way of line I 2 into about the vertical midpoint of extraction tower I4. The exact point of feed entry will vary somewhat with the feed and the conditions of operation, e. g., in some cases the point of feed entry can be near the bottom of the tower. The complex formation is exothermic and to permit the maintenance of a substantially constant temperature in tower ld, heat exchangers i6, l'! and i8 are placed therein. These heat exchangers permit operation in the range of 30 to 80 F. throughout the tower. The tower may be operated with a temperature gradient from bottom to top, in some types of operation.

Liquid HF from source 2| is passed through line 22 into vessel 23, which vessel 23 is provided with agitating means not shown. Finely divided TiF4 from storage 25 is passed by way of line 2l into vessel 23. Many methods are known for introducing a iinely divided solid into a line and conveying the material into a closed vessel, e. g.,

i, storage 2d may be equipped with a star valve at the exit thereof and line 2l may be equipped with conveying flights for moving the solid. In vessel 23, the liquid HF and the TiFi form a slurry-when as is usually the case, more Tiii is used than is soluble in the liquid HF-which slurry is passed through line 29 into an upper part of tower i4. In this illustration the TiFf. is added to the tower along with the liquid HF. However, the TiFi could be added along with the feed or could be injected into the tower directly; the treating agent may be added to the tower at one point as shown here, or at several points along the height of the tower between the point of feed entry and the top of the tower. Another method of introducing the TiF4 into the system is to add TiCli-a liquid-into vessel 23 where the chloride reacts with HF to produce TiFi. Additional liquid HF must be added to vessel 23 to participate in the reaction and leave the desired amount of liquid I-IF for use in the extrae Vlayers in separator 53.

1i tion Zone. When adding TiCli, means for venting HC1 should be provided on vessel 23.

In this illustration we use 200 volume percent of liquid HF based on the mixed feed and 2.1 mols of TiFi per mol of xylenes present in the mixed feed and 1 mol of 'IiF4 per mol of ethylbenzene present in the mixed feed. The additional TiFi based on ethylbenzene is added for the purpose of complexing with the diethylbenzene produced from the disproportionation of the ethylbenzene. We have found that a slight excess of TiF4 over the theoretical requirement is necessary in order to obtain substantially cornplete removal of xylenes from a mixed feed. However, we keep the excess addition as low as possible in order to reduce the amount of solid TiF4 present in the extractor, and subsequently in the extract phase. This is done in order to reduce side reactions and decrease the problem of handling a mixed liquid-solid system. We contact at a uniform temperature of 60 F. and at a pressure of about 10 p. s. i. g. for a total time of about l minutes in tower I4.

In order to improve phase separation, selectivity of the extraction and elimination of close boiling non-aromatic hydrocarbons from the extract phase, an inert diluent, pentane, from source 3l is added to tower I4 by way of valved line 32 at a point near the bottom of the tower. The amount of pentane added is dependent on the feed, the temperature of the extraction and the amount of liquid HF and TiFii and may vary from about to 260 vol. percent. In this illustration we use 25 volume percent of pentane based on the Ca aromatics in said feed.

Under some conditions of operation, liquid HF and TiF4 are entrained in the raffinate phase and pass out of the tower. In order to retain most of this entrained material, a stream of liquid HF can be introduced into the tower below the exit point of the raffinate phase. This wash liquid HF is introduced into tower I4 by Way of valved line 34. The amount of liquid HF from lines 29 and 34 should be adjusted to equal the desired amount of liquid HF.

The rainate phase, which includes some HF and TiFi, is passed out of tower I4 by way of line 36 into coalescer 3l. Coalescer 3l may be equipped with baffles, or may be packed with steel wool, etc. The entrained HFV and TiFi agglomerate and drain to the bottom of coalescer 3l. This recovered material is returned to tower I4 by way of valved line 38. The raffinate phase is passed out of coalescer 31 through line 4I, heater 42 and line 43 into stripper 44, which is equipped with internal heater 46. The temperature in stripper 44 is maintained high enough to remove dissolved HF and, if desired, pentane. When removing both HF and pentane, a vapor outlet temperature of about 110 F. at atmospheric pressure is suitable. The raiiinate oil which oontains the non-aromatic hydrocarbons from the feed, some ethylbenz-ene and also benzene from the disproportionation of ethylbenzene, is withdrawn from stripper 44 by Way of line 48 to storage not shown. This raffinate oil is an excellent blending stock for aviation gasoline by reason of its high octane number or the benzene can be readily recovered therefrom by distillative fractionation.

The vapors of HF and pentane are passed through line 49, cooler 5I and line 52 into separator 53. The liquid HF and pentane form two The lower HF layer is withdrawn by way of line 54 and is recycled to line 22 by lines not shown, for reuse in the process. The pentane is withdrawn by way of line 56 and is recycled to line 32 by lines not shown, for reuse in the process.

The extract phase from tower I4 consisting of liquid HF, TiFi, complex and pentane, as the predominant non-aromatic hydrocarbons, is withdrawn through line E I, and is passed through heat exchanger 62 and line 63 into decomposer 64, which is vprovided with internal heater 65. Decomposer 64 is operated at low temperature in order to decompose the complex without the introduction of side reactions, such as, interaction between the meta-diethylbenzene and xylenes to form ethylxylenes. A decomposition temperature of about 50 F. is suitable. The liquid HF is removed from the extract phase and the complex by operating decomposer 64 under vacuum. The conditions of operation of the decomposer are such that only HF passes out of the top of decornposer 64 through line 3E, and vacuum pump 6l'. rIhe HF vapors from vacuum pump El are condensed in cooler S9 and are passed into valved line 'II.

Instead of operating decomposer 64 under vacuum, the extract phase may be heated very rapidly to an elevated temperature of about 125D F. and decomposer 64 operated as a .Flash drum. Under these conditions, the extract phase and complex can be decomposed with only a slight formation of the side reaction products.

After the removal of the the bottom of decomposer 64 contains the extract hydrocarbons and solid, finely divided 'liFi precipitate. The bottoms are withdrawn through valved line I4 and are passed into lter l. Filter it may be any type of HF-resistant and vapor vtight filter, such as a plate and frame filter, a rotary filter, or a centrifuge may be used. We prefer to use a SWeetland-type lter. The TiFi is retained in the iilter and the extract hydrocarbons are passed into valved line E?. It is to be understtood that even though we show only one filter, for continuous operation two or more filters would be used.

The TiFi is removed from filter "i5 by means of a backwashing operation with liquid HF from line 1I. The slurry of liquid HF and TiFi is passed from filter f6 through valved line i3 to vessel 23 for reuse in the process.

The extract hydrocarbons which consist of xylenes, meta-diethylbenzene, some ethylxylene, and minor amounts of other polyalkylbenzenes and a very small percentage of non-aromatic hydrocarbons, predominantly pentane, are passed through valved line '.I'I, heater 'I8 and line I9 into superfractionator i which is provided with an internal heater B2. When desired, extract hydrocarbons may be withdrawn from line 'i'I through valved line 84. Superfractionator 8| is operated to produce an overhead of pentane. meta-xylene and para-xylene, which pass out of fractionator 8| by way of line 33 and are condensed in cooler Bl. The bottom product of fractionator 8I, mainly ort-ho-xylene, is withdrawn through line 5I and is passed through heater 92 and line 93 into fractionator 95, which fractionator is provided with internal heater 95. A substantially pure ortho-xylene fraction is taken overhead from fractionator 95 by way of line 9T and is sent to storage not shown. The bottoms fraction of diethylbenzene, ethylxylene and other polyalkyibenzenes is withdrawn through line 99 and sent to storage not shown. This bottoms fraction has a very high octane 13 number and makes a very suitable blending stock for aviation safety fuel.

The mixture of meta-xylene, para-xylene and pentane from cooler 81 is passed through line into a lower portion of extraction tower H3. Extractor H3 is provided with heat exchangers ||4, ||5 and H6. Extractor H3 is very similar in construction to extractor I4. In order to obtain high purity meta-xylene and high purity para-xylene, extractor i3 must provide at least 3, and preferably 4, theoretical extraction stages.

Liquid HF from source |2| is passed through line |22 into Vessel |23, which vessel |23 is provided with agitating means not shown. Finely divided TiFi from storage |26 is passed by way of line |21 into vessel |23. The slurry of HF and TiF-i in vessel |23 is passed by way of line |26 into an upper part of tower H3. The remarks made in connection with the operation of extractor ifi are also applicable to the operation of extractor I3.

In order to obtain a degree of separation such that will produce high purity meta-xylene and para-xylene, the amount of TiFi present should be at least about 2 mols per mol of meta-xylene present in the feed from line The amount of liquid HF used in extractor H3 is about 400 volume percent based on xylenes in the feed. The temperature of contacting in extractor ||3 is maintained uniformly at '10 F. for a contacting time of about minutes; pressure in tower ||3 is about 15 p. s. i. g. We prefer to operate on a mixture of xylenes and inert hydrocarbons. We attain this condition in extractor i i3 by introducing hexane from source i3! and line |32 at a point near the bottom of extractor H3. The amount of hexane added is about 100 volume percent based on xylenes charged to the tower from line H3. By introducing the hexane into the tower in this way, we obtain the desired dilution of the xylene feed and also obtain the advantages of good phase separation.

Liquid HF from line |22 is passed through Valved line |34 into the top of tower H3 in order to wash out some o the entrained TiF4 in the raffinate phase. The raffinate phase and entrained HF and 'I'iF4 is passed out of extractor H3 through line |36 into coalescer |31. The recovered HF and Tim is returned to the extractor from the bottom of the coalescer through line |36. The raffinate phase from coalescer |31 is passed through line |4|. heater |42 and line |43 into stripper |46, which stripper is provided with internal heater |46.

Stripper |44 is operated to remove overhead the HF and hexane present in the raffinate phase. The HF and hexane vapors pass overhead through line |45, are condensed in cooler |5| and pass through line |52 into separator 53. Liquid HF from separator |53 is withdrawn by line |54 and is recycled by lines not shown to line |22, for reuse in the process. Hexane is withdrawn from separator |53 by line |56 and is recycled to line |32 by lines not shown for reuse in the process. A high purity para-xylene product is withdrawn from stripper |44 by way of line |58 and is sent to storage not shown.

The extract phase consisting of liquid HF, complex and hexane is withdrawn from extractor H3 through line |6| and is passed through heater |62 and line |63 into decomposer |64. Decomposer |64 is provided with an internal heater |66. Decomposer |64 may be operated at temperatures somewhat above the boiling point of liquid HF in order to reduce the size of vessel. Appreciable isomerization of the metaxylene to an equilibrium mixture of xylene isomers takes place at temperatures much in excess of about 125 F., so we prefer to operate decomposer |64 at temperatures below about 100 F. HF vapors are taken overhead through line |66, are condensed in cooler |66 and are passed into valved line |1|.

The bottoms in decomposer |64 consist of solid, nely divided TiF4 precipitate and high purity meta-xylene. These bottoms are withdrawn through valved line |14 and are passed into iilter |16. Filter |16 is similar in construction and operation to filter 16. The meta-xylene product passes out of the iilter by way of valved line |11. The solid 'IiF4 retained in filter |16 is removed by backwashing with liquid HF from line |1|. The slurry of HF and TiF4 from filter |16 is passed through valved line |19 into vessel |23 for reuse in the process.

In order to improve the eiiiciency of operation in extractor i3, a reflux of meta-xylene is introduced near the bottom of the extractor. This refiux may be obtained from line |11 and is introduced into the extractor by way of valved line |8|. When operating with a reiiux, it is necessary to add an additional amount of TiF4 into the tower over that needed to complex the metaxylene present in the feed. We add 2 mols of TiFi to extractor I3 for each mol of meta-xylene introduced into the extractor by way of line |8|.

The product meta-Xylene is sent to storage by way of line |84. The product meta-xylene contains about mol percent of meta-xylene, between about 0.5 and 1% of hexane, and the remainder para-xylene. When it is desired to have a substantially pure aromatic hydrocarbon product, this hexane impurity can be removed by a simple distillation.

We do not wish to be bound by the above embodiment as the only way of carrying out our process. Many other variations are possible and we include these within the scope of the invention. For example, instead of decomposing the extract phase from extractor I4, the extract phase may be introduced into a second extractor and suiiicient meta-Xylene introduced into the second extractor to spring the ortho and paraxylenes from their complex. Other methods of recovering the 'IiF4 from the decomposed extract phase can be used, such as, decantation followed by recycle of a thick slurry of TiFi and aromatic hydrocarbons. Of course additional. TiFi is needed in this method of operation in order to recover the recycled aromatic hydro carbons.

This application is a continuation-in-part of our application S. N. 258,918, filed November 29, 1951, and entitled Refining of Hydrocarbon Oils with HF and TiFi.

We claim:

l. A process for separating a mixture of least two xylene isomers, which process ccmprises contacting said mixture at a temperaturpA between about 0 and 125 with between about 5 and 500 volume percent of liquid HF based on said mixture and Tilii in an amount less than about 2 mols per mol of xylenes in said mixture, separating a rainate phase from an extract phase, which extract phase comprises liquid HF, TiF4 and xylenes and wherein the ratio between the xylene isomers in said extract phase is different from the ratio in said raiinate phase and the ratios in said extract phase and said raffinate phase are direrent from the ratio in said mixture.

2. The process of claim l wherein said mixture comprises essentially meta-xylene and paraxylene.

3. A process for separating meta-xyiene from admixture with at least one other xylene isomer, which process comprises contacting said mixture at a temperature below about 90 F. with between about 100 and 300 volume percent, based on said mixture, of liquid and between about 0.5 and 2.5 mols of TiF4 per mol of meta-xylene in said mixture, separating a rainate phase from an extract phase wherein said raffinate phase has a rnolal ratio of meta-xylene to the other xylene isomers therein lower than the ratio in said mixture, and wherein the molal ratio of meta-xylene to other xylenes in said extract phase is higher than the ratio in said mixture, and recovering xylene isomers from said extract phase.

4. The process of claim 3 wherein said contacting is carried out in a continuous countercurrent apparatus and wherein the amount of Tili' is about 2 mois per mol of meta-xylene in said mixture and wherein the mixture of xylene isomers in said extract phase contains about 95% meta-Xylene.

5. A process for recovering xylenes from a mixture of Cs aromatic hydrocarbons, which process comprises contacting said mixture at a temperature below about 90 F. with between about 5 and 500 volume percent of liquid E? based on said mixture, and between about 0.5 and 2.5 mols of TiF4 per mol of xylene in said mixture, and about 1 mol of TiF4 per mol of ethylbenzene in said mixture and recovering xylene isomers from the products of said contacting.

6. The process of separating a mixture of xylene isomers, which process comprises contacting seid mixture at a temperature below about 125 in the presence of an inert hydrocarbon diluent, with between about 5 and 500 volume percent of liquid HF based on xylenes and less than about 2 mols of TiF4 per mole of xylenes, separating a rainate phase, comprising essentially said diluent and xylenes, from an extract phase, cornprising essentially liquid HF, xylenes, TiF'r and a minor amount of said diluent, and wherein the relative ratio of the xylenes in said extract phase is different from the relative ratio of xylenes in said rainate phase, and wherein both of said ratios are different from the ratio of xylenes in said mixture of xylene isomers, and recovering the xylenes from said extract phase and from said rarlinate phase.

7 The process of claim 6 wherein said inert hydrocarbon diluent is present in an amount between about 50 and 200 volume percent based on said xylene.

8. The process of claim 6 wherein said inert hydrocarbon diluent is selected from the group consisting of paranate hydrocarbons containing between 3 and 6 carbon atoms, benzene and toluene.

9. A process of recovering meta-xylene from admixture with at least one other xylene isomer and ethylbenzene, which process comprises contacting said mixture at a temperature below about 90 F., in the presence of an inert hydrocarbon diluent, with between about 100 and 300 volume percent of liquid HF based on C8 aromatic hydrocarbons and T'iF' in an amount of about 2 mols per mol of meta-xylene in said mixture, and about 1 mol per mol of ethylbenaene in said mixture, separating a rainate phase comprising essentially inert hydrocarbon diluent, benzene and Ca aromatic hydrocarbons from an extract phase comprising essentially liquid HF', Tiii, xylenes and Cm aromatic hydrocarbons and recovering from said extract phase a mixture of xylene isomers consisting predominantly of meta-xylene.

10. `The process of claim 9 wherein inert hydrocarbon dluent is present in an amount between about and 200 volume percent based on said mixture.

11. The process of claim 9 wherein the xylene isomers in said mixture are meta-xylene and para-xylene.

12. The process of recovering a nieta-xylene rich fraction from a close boiling mixture co-. prising essentially Cs aromatic hydrocarbons and non-aromatic hydrocarbons, which process comprises contacting said mixture at a temperature below about F., with between about 50 and 300 volume percent of liquid HF based on Ca aromatics in said mixture and about 2 mois of TiF; per mol of Ca hydrocarbon, separating c.. raffinate phase from an extract phase, which extract phase consists essentially of liquid HF, TiFi, xylenes and C10 aromatic hydrocarbons and contacting in a second contacting zone said extract phase, at a temperature below about 90 with meta-xyiene in a molar amount substantially equal to the amount or" xylene isomers other than meta-xylene present in said extract phase and, in the presence of about volume percent of an inert hydrocarbon diluent based on hydrocarbons present in said extract phase, separating a second raffinate phase comprising essentially inert hydrocarbon diluent and xylene isomers from a second. extra ct phase comprising essentially liquid 'liFfc meta-xylene, minor amounts of other xylene isomers and C10 aromatic hydrocarbons, and recovering from said second extract phase a high purity meta-xylene fraction.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,378,762 Frey June 19, 194.6 2,521,444 Brooke et al Sept. 5, 1950 2,528,892 Lien et al. Nov. 7, 1950 

1. A PROCESS FOR SEPARATING A MIXTURE OF AT LEAST TWO XYLENE ISOMERS, WHICH PROCESS COMPRISES CONTACTING SAID MXITURE AT A TEMPERATURE BETWEEN ABOUT 0* AND 125* F., WITH BETWEEN ABOUT 5 AND 500 VOLUME PERCENT OF LIQUID HF BASED ON SAID MIXTURE AND TIF4 IN AN AMOUNT LESS THAN ABOUT 2 MOLS PER MOL OF XYLENES IN SAID MIXTURE, SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE, WHICH EXTRACT PHASE COMPRISES LIQUID HF, TIF4 AND XYLENES AND WHEREIN THE RATIO BETWEEN THE XYLENE ISOMERS IN SAID EXTRACT PHASE IS DIFFERENT FROM THE RATIO IN SAID RAFFINATE PHASE AND THE RATIOS IN SAID EXTRACT PHASE AND SAID RAFFINATE PHASE ARE DIFFERENT FROM THE RATIO IN SAID MIXTURE. 